The use of brush elements to effect a seal between rotating members dates back to the early part of this century; for example, see U.S. Pat. No. 885,032. Although various methods are available for the production of brushes, two basic methods are now generally employed in the production of brush seals for rotating elements -- particularly as such seals are employed in turbo-machinery. The first such method can be described as the "bundle and place" method, and is exemplified by the varying techniques shown in U.S. Pat. Nos. 2,672,640; R.E. 30,206; 4,274,575 and 4,678,113. The differing procedures shown in these patents have two elements in common, they: (i) first form a bundle composed of a multitude of bristles by employing some method of securing the bristles in a substantially parallel arrangement and thereafter (ii) employ a procedure for placing the bundle onto an annular backing member and joining the bundles to the backing member, to make up the seal.
The subsequently developed method employs a winding machine to rapidly wind the wire onto a mandrel; wherein (i) the mandrel itself may be the backing member which will form the brush seal, i.e., as shown in U.S. Pat. Nos. 4,204,629, 4,642,867 and 4,732,339, or (ii) the wound mandrel is used to hold the multitude of bristles for subsequent placement onto the annular backing ring, as shown in U.S. Pat. No. 4,730,876. Initially, such winding procedures appeared to offer significant advantages because of their suitability to rapid production and automation. However, they have proven unsuitable in the production of small diameter brush seals, because long lengths of wound bristles are unsuitable to achieving the required bristle inclination relative to the backing member. Moreover, winding around the backing member dictates that a significant portion of the wrapped wires be scrapped--after cutting. When employed in turbine engines, the strands which form the brush are normally expensive, high temperature, exotic metal alloys or ceramics--such that the scrapped material adds significantly to the cost of production. Additional disadvantages of such winding procedures are noted in U.S. Pat. No. 4,678,113.
To overcome such disadvantages, the '113 Patent discloses a manual "bundle and place" method which requires: the formation of a self-supporting ribbon (or tape) composed of many fine strands of wires--adhesively bonded together, cutting the tape into a plurality of tufts, securing the tufts to a backing plate, and removing the adhesive from the portion of the tape projecting from the backing plate. A variant procedure, better adapted to automation, is disclosed in a related patent, U.S. Pat. No. 4,642,867, the disclosure of which is incorporated herein, by reference. The method shown in '3 867 Patent delays the cutting step (of the '113 Patent) by feeding the adhesively bonded tape onto the backing ring (which is fitted onto a rotating work bed), clamping a portion of the tape to the backing ring--utilizing a finger clamp for each tape width, and then cutting the tape to form a bundle of strands clamped to the ring. After the required number of bundles have been clamped around the circumference of the backing ring, clamping rings are fitted onto the backing ring to permit the removal of the clamping fingers. Thereafter, a second cover plate is placed onto the work--sandwiching the bundles between the two plates. The outer periphery of the annular sandwich is then welded, to secure the two side plates with the bundles therebetween, to form a brush seal.